1. Field of the Invention
This invention relates to a novel optical information recording medium and the recording of information thereon. More particularly, the present invention relates to an information recording medium, preferably in the form of a disk, suitable for use with optical recording and playback apparatus, which recording medium is stable yet readily and accurately erasable.
2. Description of the Prior Art
Various optical recording media and methods for recording information thereon are known to the prior art. For example, the recording of information in the form of deformations or ripples in a thermoplastic film is known, with techniques for achieving such deformations involving the steps of (1) forming a charge pattern on the surface of the thermoplastic film in accordance with the information to be recorded, (2) heating the thermoplastic film to its melting point so as to permit the electrostatic forces produced by the charges to form a deformation pattern in the thermoplastic film corresponding to the charge pattern and thus to the information to be recorded, and (3) then cooling the thermoplastic film below its melting point to fix the thus formed deformation pattern in the film. Reading of the information represented by the deformation pattern in the thermoplastic film may be accomplished using well known optical techniques. See, e.g., U.S. Pat. No. 3,952,146.
Techniques for erasing the deformation pattern involve reheating the thermoplastic film above its melting point to a significantly higher termperature than during recording in order to permit surface tension to smooth out the surface. Selective erasure may be accomplished by confining the heating to a selected area. After cooling, another deformation pattern may be recorded in the thermoplastic film.
Clemens, in U.S. Pat. Nos. 3,842,194; 3,842,217; and 3,909,517; describes a conductive video disk comprising a molded plastic disk having video and audio information in the form of geometric variations in a spiral groove in the disk surface. These disks are coated first with a conductive material, such as a metal, which acts as a first electrode, and then with a dielectric layer, such as an inert polymer layer. A metal-tipped stylus acts as a second electrode of a capacitor and the information signals are monitored by the stylus which notes changes in capacitance between the stylus and the disk surface as the information, in the form of depressions, passes beneath the stylus when relative motion is established between the disk and the stylus.
Optical recording methods in which light from a laser is focused upon the surface of a recording medium with sufficient intensity to cause ablation of surface material have also been proposed. In such methods, an information representative pattern of pits may be formed in the surface of the recording medium by suitably controlling the intensity of the focused light in accordance with the information to be recorded while relative motion is established between the recording medium and the focused light spot.
For instance, in recent years, attention has been increasingly paid to the information recording method in which information is written in a thin film of metal or the like formed on a substrate by using a laser ray or beam. According to such a method, the information recording has been accomplished by forming holes or recesses in the metallic thin film under the action of a thermal energy beam such as a laser ray. See, e.g., U.S. Pat. No. 4,238,803.
Spong, U.S. Pat. No. 4,097,895, describes a recording medium which comprises a light reflecting material, such as aluminum or gold, coated with a light absorbing layer, such as fluorescein, which is operative with an argon laser light source. The thickness of the light absorbing layer is chosen so that the structure has minimum reflectively. An incident light beam then ablates, vaporizes or melts the light absorbing layer, leaving a hole and exposing the light reflecting layer. After recording at the wavelength of the recording light, maximum contrast between the minimum reflectance of the light absorbing layer and the reflectance of the light reflecting layer exists. In this regard, note also U.S. Pat. No. 4,219,826.
Carlson, in U.S. Pat. No. 3,475,760, discloses a system for directly recording information in a thermoplastic film as a deformation by using a high energy laser scanning beam of small diameter. Erasure of the film deformation is accomplished by recording over the information to be erased using a similar laser beam but with a much smaller scan line spacing, preferably so as to provide overlap of the scan lines. Suitable thermoplastic films are disclosed as including vinyltoluenebutadiene, polystyrene ortho-terphenyl, polyethylene, and nitrocellulose.
The recording medium, of course, is one of the key elements in any optical and/or audio recording system, and this is particularly true in the home entertainment market where erasable recording disks would be a very desirable product, provided the recording disks could match the commercial magnetic tapes with regard to the technical parameters and the economics of a recording medium. Although many different media have been investigated for possible use in the various aforediscussed recording systems, and in particular the laser systems, a suitable recording medium or disk which is stable and economical, yet readily erasable when desired, has heretofore not been provided. Such a recording medium, and in particular if in the form of a disk, would be readily accepted and would fill the void in the video recording marketplace. The search for improved, erasable optical recording media is continuously ongoing.
Accordingly, it is a major object of the present invention to provide a novel optical recording medium which is stable, yet readily and accurately erasable when desired.
It is yet another object of the present invention to provide a novel erasable recording medium upon which information is recorded as a deformation and wherein said information can easily be erased to thereby provide a blank recording medium upon which information can be recorded.
It is still another object of the present invention to provide an erasable recording medium, particularly useful for video recordings, which comprises a polymeric layer exhibiting specifically selected properties to render the recording and erasing of information from the recording medium most effective and economic.
It is still another object of the present invention to provide an erasable recording disk comprising a uniquely suited polymer layer which renders the recording and erasing of information technically accurate and economically expedient.
These and other objects, as well as the scope, nature and utilization of the invention, will be apparent to those skilled in the art from the foregoing description and the appended claims.